Portable Document Format (PDF) is a file format created by Adobe® Systems for document exchange. PDF is used for representing two-dimensional documents in a manner independent of the application software, hardware, and operating system. Among the features supported by PDF is transparency. Basic transparency is an effect that lets the viewer see through an object. End-users can specify the transparency attributes of selected page items. Opacity is the converse of transparency. Each is typically expressed as a percentage, where 0% relates to completely clear, i.e. not transparent, and 100% relates to completely opaque, i.e. completely invisible to the end-user. Page items can have individual opacities assigned to them. Blending mode defines how the background (backdrop) and foreground (source) colors interact.
Starting with version 1.4 of the PDF standard, transparency, (including translucency), is supported. This is a very complex model, requiring over 100 pages to document. A key source of complication is that PDF files may contain objects with different color spaces, and blending such objects can be difficult. PDF supports many different blend modes, not just the most common averaging method. In addition, rules for compositing many overlapping objects allow choices, such as whether a group of objects are to be blended before being blended with the background, or whether each object in turn is to be blended into the background.
PostScript®, a registered trademark of Adobe® Systems, is a page description programming language created by Adobe for the electronic and desktop publishing areas. PostScript is the language used for driving a wide variety of commercially available laser printing devices. The PostScript language does not inherently support transparency. This presents a problem with printing PDF files on a PostScript-enabled printing device.
Accordingly, what is needed is in this art are increasingly sophisticated systems and methods which emulating transparency in a PostScript-enabled printer.